South Canterbury, a region half-way down the east coast of the South Island of New Zealand, has been working since June 2011 to raise NZ$2.7 million. Their goal: to buy an MRI machine for Timaru Hospital. According to the local paper, the appeal was only $250 000 off their goal as of the 27th March.

Currently, patients need to travel either 2 hours north to Christchurch or two and a half hours south to Dunedin to get an MRI scan done.

For a region of 55,318 people, fundraising just under $2.5 million within 10 months shows the value they place on having a local MRI scanner.

An MRI scanner. Source: Creative Commons (Tomas Vendis)

Magnetic Resonance Imaging. It’s a way to let doctors see inside your head, literally. Pictures that show the soft tissue of the body in slices, like the ones shown below, are produced.

MRI scans measure signals from Hydrogen atoms of water (H2O) in the body. Healthy and damaged tissue contain different amounts of water.

An MRI image shows the quantity of water present in different areas of body tissue using different shades of grey. This allows damaged tissue to be spotted. Injection of contrast agents (dyes) into the body is also used to get a clearer picture.

How does it work?

MRI technology exploits knowledge of atomic properties such as nuclear spin to create a recognisable picture of the brain.

The technology is based on the fact that damaged tissue and healthy tissue have different amounts of water in them. The hydrogen (H) atoms in this water are spinning in random directions around their individual magnetic fields.

If you apply a strong magnetic field to the body, all of the individual magnetic fields of the H atoms in water line up. The only difference between the spins is whether they are rotating clockwise or anticlockwise around the magnetic field.

This leaves a couple of H atoms out of every million that don’t cancel each other out (1 atom spinning clockwise cancels an atom spinning anticlockwise). This is still a considerable number of H atoms.

A radio frequency specific to Hydrogen is then applied to the body, which excites the H atoms with lots of energy for a short period of time. The atoms then emit this energy at a certain frequency.

While the radio frequency is applied, doctors can manipulate three gradient magnets within the machine to define the area that an image is produced from. This area or ‘slice’ pictured can be angled from any direction, a distinct advantage over other imaging techniques.

A computer watches all the frequencies emitted by the excited H atoms and maps them as an image. Where lots of H signals were seen, there was lots of water. The shade of grey on the MRI is proportional to the amount of water in that region.

Applications of MRI

A doctor can now look at the map of grey regions and detect if there are abnormalities.

Diffusion MRI technology is being used to map connectivity of different regions of the brain.

Because of the superiority of MRI technology in imaging soft tissue, MRI scans are being used to specifically locate tumours within the body in preparation for radiation therapy. The MRI scans will show the exact location, size, shape and orientation of the tumour. This allows for extremely precise radiation therapy to be applied to the cancer tissue.

A look at an MRI scanner from the technician's office. Source: Creative Commons (US Navy)

What’s it like for a patient?

Before going into an MRI machine, a patient is asked to remove all metal they are wearing. This includes zips, watches and credit cards. Anything magnetic inside the machine can be repelled by the magnetic fields and become a dangerous projectile.

Patients have to remain very still for between 20-90 minutes while the MRI machine makes a lot of noise. Any movement will blur the MRI image and a new scan will have to be made.

The noise inside the machine was described to me as continual hammering right beside your head. This is a result of rising electric current from the main magnetic field in the machine interacting with the three gradient magnets. Patients are generally given ear plugs.

To avoid attacks of claustrophobia, there is a system of mirrors angled so that the patient see out of the machine.

Unlike other imaging technologies, MRI machines do not use ionizing radiation.

Once a patient emerges from the MRI machine the body and its chemistry reverts to normal. The dye may take a bit longer to pass through the system, but there are no known biological hazards that result from exposure to magnetic fields of the strength used in MRI machines.